class Solution {
    public:
        string longestPalindrome(string s) {
            int n = s.size();
            vector<vector<bool>> dp(n,vector<bool>(n));
            int begin = 0,lenth= 0;
            for(int i = n-1 ; i >= 0 ; i--){
                for(int j = i; j < n ; j++){
                    if(s[i] == s[j]){
                        dp[i][j] = i+1 < j ? dp[i+1][j-1] : true;
                    }
                    if(dp[i][j] && j-i+1 > lenth){
                        begin = i;
                        lenth = j-i+1;
                    }
                }
            }
            return s.substr(begin,lenth);
        }
    };